1. Field of the Invention
The present invention relates to a recording medium.
2. Description of the Related Art
To improve the fastness of recorded images, metal ions or metal salts have been provided in an ink receiving layer of a recording medium used for inkjet recording or the like. Japanese Patent Laid-Open No. 2000-177235 discloses a recording medium obtained by simply adding a water-soluble metal salt or a slightly soluble metal compound to an ink receiving layer containing hydrated alumina to improve the fastness of recorded images, ink absorbency, and ink fixing property and to achieve high color density and the like. Japanese Patent Laid-Open No. 61-57380 discloses a recording medium that contains a porous inorganic pigment, a cationic resin, and a magnesium compound whose solubility in water is 1% or less at room temperature to improve water resistance and light resistance and to achieve high color density. Japanese Patent Laid-Open No. 63-166586 discloses that silica is subjected to surface treatment with a compound or a salt of metal ions having at least univalence to improve the fastness of recorded images. This means that silica is subjected to surface treatment with a metallic soap, a metal hydroxide, a metal salt, or a metal oxide. It is disclosed that silica is subjected to surface treatment by adding a metal salt to silica at 90° C., which is a heating condition when silica is synthesized, and then by aging it for 20 minutes.
However, the inventors of the present invention found that the above-described related technologies contain the following problems. For the recording medium disclosed in Japanese Patent Laid-Open No. 2000-177235, a water-soluble metal salt is merely impregnated or dispersed thereinto. After printing, such a water-soluble metal salt does not remain on the surface of the ink receiving layer and easily enters the ink receiving layer together with a solution. As a result, the image fastness is slightly improved, but a coloring material easily enters the ink receiving layer, which causes the image to have insufficient optical density. For the recording medium disclosed in Japanese Patent Laid-Open No. 61-57380, the image fastness is improved, but the effect is not sufficiently high. It is believed that this is because a dye is not always present near magnesium compound particles after printing and thus the effect to be produced by addition of a magnesium compound is not sufficiently achieved. In the method for subjecting silica to surface treatment disclosed in Japanese Patent Laid-Open No. 63-166586, since a metal is present in a state in which the metal is easily soluble in water, a metal contained in a coating solution is eluted, which easily increases the viscosity of the coating solution. Furthermore, it is difficult to improve the color development property of a recording medium manufactured. It is believed that this is because the coating solution easily aggregates due to the eluted metal ions, which decreases the transparency of the ink receiving layer.